The present invention relates to ocean thermal-energy conversion ("OTEC"), metal hydrides and superconductors.
Historically, closed-cycle heat engines have required working fluids such as ammonia or chloroflurohydrocarbons ("Freon") which are liquid during part of the engine cycle. Typically the fluid is pumped through a heat exchanger (or evaporater), where it is vaporized by the heat source being utilized. The vapor drives a turbine and the vapor must then pass through a second heat exchanger (the condenser) where the vapor returns to a liquid state before the cycle is repeated.
In the recent past, it has become possible to build heat engines utilizing metal hydrides which evolve hydrogen gas when they are heated and reabsorb the hydrogen when they are cooled. Such metal hydride heat engines are more efficient that conventional heat engines. In the metal hydride system, the hydrogen is evolved from a solid to a gaseous state under pressure and then is reabsorbed by a solid, and there is no requirement that it pass through a liquid phase. Larger changes in pressure at the same temperature differentials are possible utilizing metal hydrides than in conventional heat engines that use liquid/vapor working fluids.
Metal hydrides are formed by bringing gaseous hydrogen (H.sub.2) in contact with a metal (M). The chemical reaction during which metal hydrides are formed is reversible. If the hydrogen gas pressure is above the equilibrium pressure (which is a function of the metals involved and temperature), the reaction between the hydrogen and metal occurs and the metal hydride is formed. Below equilibrium pressure, the metal hydride decomposes into the metal and gaseous hydrogen.
Formation of a metal hydride is an exothermic reaction; that is, heat is given off when the hydride is formed by reaction of hydrogen with the metal. Decomposition of the metal hydride back into metal and hydrogen gas requires the continuous addition of heat. Thus, by selection of appropriate metals and pressure conditions, it is possible to cause hydrogen to be given off by heating the metal hydride, and, alternatively, to cause hydrogen to be absorbed by cooling the hydride bed. Metal hydrides are further discussed in the article "Hydrogen Storage In Metal Hydrides," by J. J. Reilly and Gary D. Sandrock, Scientific American, February, 1980, which is incorporated herein by this reference. Additional background information useful in understanding the present invention is contained in the following United States patents and publications, all of which are incorporated herein by this reference:
U.S. Pat. No. 4,425,318 to Maeland et al. for "Hydriding Body-centered Cubic Phase Alloys At Room Temperature";
U.S. Pat. No. 4,440,736 to Maeland et al. for "Titanium-based Body-centered Cubic Phase Alloy Compositions in Room Temperature Hydride-forming Reactions Of Same";
U.S. Pat. No. 4,440,737 to Libowitz et al. for "Room Temperature Reaction Of Vanadium-based Alloys With Hydrogen";
U.S. Pat. No. 4,600,525 to Baker et al. for "Hydrogen Sorbent Flow Aid Composition and Containment Thereof";
"A Technique for Analyzing Reversible Metal Hydride System Performance," by P. N. Golben and E. Lee Huston, presented at the International Symposium on the Properties and Applications of Metal Hydrides, Toba, Japan, May 30-June 4, 1982;
"Closed-cycle Hydride Engines," by Thomas E. Hinkebein, Clyde J. Northrup and Albert A. Henckes, Sandia Laboratories, December, 1978;
"Use of Vanadium-based Solid Solution Alloys in Metal Hydride Heat Pumps," by G. G. Libowitz and A. J. Maeland, Allied-Signal Corporation; and
"A Solar-Powered Diaphram Pump," by R. Burton, Solar Energy volume 31, number 5, pp. 523-525, 1983.
It has been recognized that temperature differentials in ocean water may be utilized to generate electricity, and efforts have been undertaken to accomplish that generation on a practical basis. Such efforts are summarized in "Power From The Sea," by Terry R. Penney and Desikan Bharathan in the January, 1987 issue of Scientific American, which is incorporated herein by this reference. As is well-recognized in the field of ocean thermal energy conversion (and as is illustrated in the drawing appearing on page 91 of the Penney and Bharathan article), one of the principal costs of OTEC systems is the expense associated with pipelines to carry warm and cold water to and from the generating facility. This is because a very substantial quantity of water must be utilized to operate a conventional OTEC system. Another problem associated with OTEC, as well as other conventional power generation systems, is the storage of electrical power generated by the system until it can be used, particularly in systems which generate power at a constant rate but supply distribution networks which have power demands which vary widely over time, as, for instance, during a twenty-four hour period.
An additional problem associated with closed-cycle heat engines utilizing chloroflurohydrocarbons is concern about the adverse environmental impact of atmospheric release of such materials, particularly including possible damage to the earth's ozone layer. Such concerns have resulted in calls for reduced use of chloroflurohydrocarbons, which may make it difficult or impossible to construct OTEC or other systems utilizing such working fluids. Finally, chloroflurohydrocarbon working fluids normally cannot be made to travel long distances through pipes without condensing before condensation is desired.